Thursday, August 25, 2016

Thought to
be at least 1.3 times mass of Earth, planet lies within ‘habitable’ zone of
Proxima Centauri, raising hopes for life outside our solar system!

The search
for life outside our solar system has been brought to our cosmic doorstep with
the discovery of an apparently rocky planet orbiting the nearest star to our
sun.

Thought to
be at least 1.3 times the mass of the Earth, the planet lies within the
so-called “habitable zone” of the star Proxima Centauri, meaning that liquid
water could potentially exist on the newly discovered world.

Named
Proxima b, the new planet has sparked a flurry of excitement among
astrophysicists, with the tantalizing possibility that it might be similar in crucial respects to Earth.

“There is a
reasonable expectation that this planet might be able to host life, yes,” said
Guillem Anglada-Escudé, co-author of the research from Queen Mary, University
of London.

Eamonn
Kerins, an astrophysicist at Jodrell Bank Centre for Astrophysics, was among
those enthusiastic about the discovery. “Finding out that the nearest star to
the sun hosts not just a planet, not just an Earth-sized planet, but one which
is in the right location that it could support life - and there are a lot of
caveats there - really underscores that not only are planets very common in our
galaxy, but potentially habitable planets are common,” he said.

Proxima b
may be the closest of the thousands of exoplanets - which are planets orbiting
stars outside our solar system - discovered to date, but at 4.2 light years
away the prospect of quick visit to find any Proximese aliens is still remote.
Based on spacecraft today, a probe launched now would take around 70,000 years
to reach the new planet.

Writing in
the journal Nature, an international team of researchers describe how they
discovered the planet after scrutinising data based on the light emitted by
Proxima Centauri, collected using instruments at the European SouthernObservatory in Chile.

“What we
basically do is measure how the star is moving,” said Anglada-Escudé. “If you
have a planet around a star, the planet is also pulling the star a bit so you
see the star is moving. It is going towards you and away from you,
periodically.”

This
movement affects the color of light detected from the star - as it the star
moves slightly towards us we see the light as being slightly bluer - as it
moves away the light appears a little redder. The frequency of this motion
relates to the duration of the planet’s orbit, and hence its distance from the
star, while the magnitude of the motion provides information about the planet’s
mass.

While
analysis of data collected before 2016 hinted at the presence of a planet, it
took a further intense round of data collection earlier this year before the
discovery could be confirmed.

Taking 11.2
days to travel around Proxima Centauri, the planet orbits at just 5% of the
distance separating the Earth and the sun. But, researchers say, the planet is
still within the habitable zone of its star because Proxima Centauri is a type
of red dwarf known as an M dwarf - a smaller, cooler, dimmer type of star than
our yellow dwarf sun.

Whether the
planet could harbour life, however, is matter of debate.

Red dwarfs
are generally very active stars, emitting powerful solar flares, with Proxima b
receiving greater doses of high-energy radiation than reaches Earth from our
sun. “Because they tend to have a lot of these flares and things like that, it
makes it very difficult for [planets] to keep an atmosphere - these flares just
blow the atmosphere away,” said Don Pollacco, professor of astrophysics at the
University of Warwick, who was not involved in the research. But, he adds,
Proxima Centauri is only a moderately active red dwarf, potentially making its
environment less hostile than other such stars. Whether the star’s activity
when it was younger could have stripped Proxima b of an atmosphere remains to
be discovered, while it is also unknown if the planet has a magnetic field
which could potentially protect it from such radiation.

The planet
has other characteristics that could affect its potential to host life.

The
research reveals that if the planet’s temperature were down to its sun alone,
its surface would be, on average, a chilly -40C. “It seems cold, but then if
you look at the same numbers for Earth you would get minus 20, minus 30C,” says
Anglada-Escudé. “What keeps Earth warm is basically that it has an atmosphere
and an ocean,” he adds, pointing out that should the newly discovered world
also boast an atmosphere, its temperature would likewise be higher.

And there’s
more. It is very likely that the new world is tidally locked to Proxima
Centauri (just as our own moon is to Earth) with only one side of the planet
ever catching the star’s rays.

“If you are
standing [on the side] looking at the star, you are quite warm,” said Pollacco.
“If you are on the other side it is bloody cold - continual night.”

Anglada-Escudé
is sanguine. If the planet has an atmosphere or an ocean, he says, the
redistribution of heat could be possible. “Even if you have tidal lock, you
have a lot of circulation - it is like jet streams on Earth.”

But
Pollacco believes discussion about the habitability of the new planet is
somewhat premature, “These observations tell you nothing about the planet
itself, it is important to realise that,” he said, pointing out that there is
no evidence that the planet has an atmosphere, or any water.

Anglada-Escudé
admits that there is plenty to be unpicked about the new world. While its mass
is thought to be at least 1.3 times that of the Earth, its size, and hence
density, is unknown, meaning that scientists can only make an educated guess
that it is likely to be rocky based on the types of exoplanets that have
previously been detected around other small stars.

And there
are other mysteries to solve. The planet’s location is also puzzling scientists,
who say it is unlikely that the planet formed in its current location given
that there would have been little planet-forming material available so close to
the star. “What we suspect is that the planet forms somewhere else, or the raw
materials, the dust or the rocks or the ice, condense somewhere else and then
ended up there through some migration process,” said Anglada-Escudé. He points
out that if the planet formed farther away from the star and migrated to its
current position, it is likely to be a “water-world”, whereas if it formed in
its current location from dust that migrated, it is likely to be very dry
unless water was later delivered to the planet by a comet or other body.

While
Pollacco describes the new discovery as symbolic, he believes the planet’s
potential for hosting life could remain a mystery for many years to come, not
least because the chances of seeing the planet pass in front of its star - an
observation, known as a transit, that is crucial to unravelling the planet’s
size and make-up - are low.

Anglada-Escudé
is rather more optimistic. Even if a transit cannot be seen, he believes other
techniques could shed light on the nature of the planet. “There are reasonable
expectations that this planet can be detected with direct imaging within the
next 10 years,” he said, adding that it might also be possible to design a
space telescope to orbit around the Earth and look at the new world.

And with
Proxima b just an interstellar stone’s throw away, he believes the new
discovery could inspire a wave of creativity in designing approaches for
probing the planet further.

“Just the
discovery, the sense of exploration, of finding something so close, I think it
is what makes [it] very exciting,” he said.

This article was amended on 24 August 2016.
The planet orbits at 5% of the distance separating the Earth and the sun, not a
fifth as an earlier version said.

AWAKENING FOR ALL!!!

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